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For disk and network input/output operations, Confidential VM uses a specific area
in memory called the Software Input Output Translation Lookaside Buffer
(SWIOTLB), which has a default size of 64 MB. The SWIOTLB is part of the
total available RAM on the guest.
To check if a Confidential VM instance has encountered the swiotlb buffer is full
error, connect to the instance and run the following command to query the
dmesg logs:
dmesg|grep'swiotlb buffer is full'
To resolve this issue, increase the SWIOTLB size. Before increasing the size,
ensure that the guest has enough RAM for the SWIOTLB and the operating system.
Increase the SWIOTLB size
To increase the size of the SWIOTLB, append the following line to
/etc/default/grub:
The following example shows how to increase the size of the SWIOTLB to
512 MB:
GRUB_CMDLINE_LINUX_DEFAULT=".... swiotlb=262144"
Based on the Ubuntu version, you need to update the string in the grub
file. For example, if you use Ubuntu 18.04, you need to update the
GRUB_CMDLINE_LINUX string instead of the GRUB_CMDLINE_LINUX_DEFAULT
string.
[[["Easy to understand","easyToUnderstand","thumb-up"],["Solved my problem","solvedMyProblem","thumb-up"],["Other","otherUp","thumb-up"]],[["Hard to understand","hardToUnderstand","thumb-down"],["Incorrect information or sample code","incorrectInformationOrSampleCode","thumb-down"],["Missing the information/samples I need","missingTheInformationSamplesINeed","thumb-down"],["Other","otherDown","thumb-down"]],["Last updated 2025-03-05 UTC."],[[["Confidential VMs utilize a memory area called SWIOTLB for disk and network I/O, which defaults to 64 MB and is part of the guest's total RAM."],["The `swiotlb buffer is full` error can be checked by connecting to the instance and querying the `dmesg` logs using `dmesg | grep 'swiotlb buffer is full'`."],["To resolve the `swiotlb buffer is full` error, you need to increase the SWIOTLB size by appending `swiotlb=\u003cSIZE_IN_BYTES\u003e` to the `GRUB_CMDLINE_LINUX_DEFAULT` line in `/etc/default/grub` (or `GRUB_CMDLINE_LINUX` for Ubuntu 18.04)."],["After modifying the grub file, you need to regenerate the `grub.cfg` file by using either the command `sudo update-grub` for Ubuntu, or the commands `grubcfg=\"/etc/grub2-efi.cfg\"`, `cp $grubcfg $grubcfg.bak` and `grub2-mkconfig -o $grubcfg` for other distros, followed by a reboot."]]],[]]
